The A’s got Johnson on Monday for infielder Jemile Weeks and a player to be named, capping a busy day for general manager Billy Beane.

Balfour became a free agent after the season and is expected to command a multiyear deal. While Beane expressed confidence he could fill the ninth-inning duties from within, he opted for a trade — a common December practice for the GM and low-budget club.

The 30-year-old Johnson converted 50 of 59 save opportunities in 2013, going 3-8 with a 2.94 ERA. He was tied with Atlanta’s Craig Kimbrel for the major leagues saves lead.

Also Monday, free-agent left-hander Scott Kazmir agreed to terms on a $22 million, two-year contract with Oakland, a person with knowledge of the negotiations said.